Discovery dates

Most definitely, and at Able2know we often discuss the merits of each and every claim in Latin (ad nauseam with correct spelling) and with much gusto.

Here's my fave:

http://environmentalchemistry.com/yogi/periodic/year.html

Arsenic April 1 1250 seems a tad late in my view.

http://www.lenntech.com/periodic-chart-elements/discovery-year.htm

Where does it say that arsenic was discovered on April 1?

Here's what I've found:

Hydrogen by 12 May 1766
Helium 26 March 1895
Lithium by 27 January 1818
Beryllium by 15 February 1798
Boron 21 June 1808
Carbon (ancient)
Nitrogen by 12 September 1772
Oxygen 1 August 1774
Fluorine by 30 June 1771
Neon by 30 June 1898
Sodium by 19 November 1807
Magnesium by 30 June 1808
Aluminum by 31 May 1825
Silicon have not found
Phosphorus have not found
Sulfur (ancient)
Chlorine have not found
Argon by 13 August 1894
Potassium by 19 November 1807
Calcium by 30 June 1808
Scandium by 22 March 1879
Titanium have not found
Vanadium have not found
Chromium by 31 July 1798
Manganese have not found
Iron (ancient)
Cobalt have not found
Nickel by 26 October 1751
Copper (ancient)
Zinc (medieval)
Gallium 27 August 1875
Germanium 6 February 1886
Arsenic (medieval)
Selenium by 9 February 1818
Bromine by 3 July 1826
Krypton 30 May 1898
Rubidium have not found
Strontium by 30 June 1808
Yttrium by 30 June 1794
Zirconium have not found
Niobium by 26 November 1801
Molybdenum have not found
Technetium have not found
Ruthenium have not found
Rhodium by 14 June 1804
Palladium by 31 July 1802
Silver (ancient)
Cadmium have not found
Indium have not found
Tin (ancient)
Antimony (medieval)
Tellurium 13 April 1782
Iodine by 31 May 1811
Xenon 12 July 1898
Cesium have not found
Barium by 30 June 1808
Lanthanum by 30 November 1838
Cerium have not found
Praseodymium have not found
Neodymium have not found
Promethium have not found
Samarium 28 July 1879
Europium have not found
Gadolinium have not found
Terbium have not found
Dysprosium by 27 April 1886
Holmium have not found
Erbium have not found
Thulium have not found
Ytterbium by 22 July 1878
Lutetium have not found
Hafnium by 11 December 1922
Tantalum by 31 March 1802
Tungsten have not found
Rhenium by 30 June 1925
Osmium by 10 October 1803
Iridium by 10 October 1803
Platinum (medieval)
Gold (ancient)
Mercury (ancient)
Thallium have not found
Lead (ancient)
Bismuth have not found
Polonium 13 July 1898
Astatine by 15 October 1940
Radon by 23 June 1900
Francium have not found
Radium by 26 December 1898
Actinium have not found
Thorium have not found
Protactinium by 15 March 1913
Uranium have not found

Since this is getting long and tedious, I'm not going to include the elements beyond Z=92. Do you think you could fill in the gaps and try to find the dates when the elements were actually found?

I think that to call those dates "discovery dates" is a mistake. The scientific process doesn't work like that. A scientist doesn't say "On 13 July 1898 I was in my lab and I moved a couple of books and there it was! Polonium!". For example helium. Helium was first discovered by two astronomers, the French scientist Pierre Janssen and the English astronomer Norman Lockyer who observed a bright yellow line in the in spectrum of the Sun during the solar eclipse of 1868 (which was named the D3 line). In 1871 Lockyer explained it by the presence of a new element in the Sun. On 26 March 1895 British chemist William Ramsay isolated helium on Earth the gas liberated from the mineral cleveite, in the spectrum of which he noticed a bright-yellow line that matched the D3 line observed in the spectrum of the Sun.